This invention relates to propulsion units for marine vessels and, more particularly, to propulsion units for marine vessels which are supported by a strut extending from a hull of a vessel.
Conventional propulsion arrangements for surface ships are generally internally powered shaft-driven propeller-type systems in which the propeller shaft passes through the ship's hull at an angle to facilitate the layout of the propulsion plant equipment within the ship due to the typical hull geometry. Such angled shafting reduces propeller efficiency. Moreover, the typical geometry of the hull of a marine vessel does not provide uniform inflow to such a propeller which also reduces propeller efficiency.
The patents to Kirin U.S. Pat. No. 1,595,949, Pierce U.S. Pat. No. 1,910,561, Billing U.S. Pat. No. 2,372,247 and Waterval U.S. Pat. No. 2,691,356 disclose coaxial dual propeller drives for ships. The Waterval patent describes a coaxial dual propeller drive arrangement in an offset pod supported by a strut through which a mechanical drive connection is provided. The patents to Clark U.S. Pat. No. 3,528,383, Lemont U.S Pat. No. 5,292,088, Lashman U.S Pat. No. 5,634,423 and Itima et al. U.S. Pat. No. 5,848,922 disclose shrouded propeller arrangements for marine vessels arranged to produce a desired flow of water to the propeller. The Tank et al. U.S. Pat. No. 1,691,593 discloses an aircraft propulsion pod supported by struts from an aircraft wing powering a pusher propeller and containing an internal fan to pump air to the cylinders of the drive motor. The Niemi U.S. Pat. No. 5,679,045 discloses a propulsion device supported by a strut in spaced relation to a ship's hull in which electrical power is transmitted through the strut to an electric motor in the pod which drives a propeller.